Spontaneous ignition of oil sands

Abstract

In planning oil recovery by in situ combustion, one problem is how to ignite the formation. Ignition can be effected by heating the formation around the injection well or by injecting an easily reacting chemical compound prior to injecting air. In some field experiments (General Petroleum's project in S. Belridge and Shell's field test in W. Venezuela), no special measures appeared to be necessary. The formations ignited spontaneously when air was injected for a prolonged period to determine the gas-flow distribution in the formation underlying the test site. This showed that at least in some oil reservoirs, oxidation rate of the crude at reservoir temperature is high enough to heat the reservoir locally to ignition temperature in a reasonable short time. Spontaneous-ignition times depend on the initial formation temperature and the reactivity of the crude, and may vary from a few weeks to several months. For this reason, it is desirable to have an estimate of how long spontaneous ignition will take, so that ignition by artificial means may be considered soon enough. A method for predicting the ignition time on the basis of measured oxidation rates of the crude is given.